Manufacture of polyvinyl aromatic acetals and pigments therefrom



Patented Feb. 9, 1954 MANUFACTURE OF POLYVINYL AROMATIC ACETALS AND PIGMENTS THEREFROM Louis Amde Lantz and Arthur Schofield, Manchester, England, assignors to The Calico Printers Association Limited, Manchester, England, a British company No Drawing. Application September 18, 1950, Serial No. 185,504

Claims priority, application Great Britain May 13, 1 44 14 Claims. (01. 260-41) This invention relates to manufacture of polyvinyl aromatic acetals and pigments therefrom; and it comprises a process wherein an aqueous solution of a polyvinyl alcohol or derivative thereof, having a concentration ranging from about 1 to 20 per cent by weight, is condensed at temperatures within the range of about 1 to 80 C., with at least one aldehyde of the benzene and naphthalene series, said aldehyde being in highly dispersed form, in the presence of an acetalizing catalyst and in proportions producing a waterinsoluble condensation product, thereby producing in situ a precipitate of an aromatic acetal of said polyvinyl alcohol in extremely finely-divided form capable of being dyed directly in light iast bright colors; all as more fully hereinafter set forth and as claimed.

The present application is a continuation-inpart of our copending application, Serial Number 592,918, filed May 9, 1945, now abandoned. This prior application discloses the same procedures for making the polyvinyl aromatic acetals and corresponding pigments which are herein described and claimed, but more generally. In the present application our processes are described more specifically and with additional examples and the limits of our invention are more closely defined.

Various processes have been proposed in the art for making polyvinyl acetals. In these processes polyvinyl alcohols have been condensed with various aldehydes, usually in the presence of an organic solvent, the solutions of polyvinyl acetals thus formed being usually precipitated by the addition of water or other non-solvent in order to recover the polyvinyl acetals. In these procedures a considerable amount of difficulty has been encountered owing to the tendency of the polyvinyl acetals to be precipitated in the form of lumps or coarse particles which are incapable of being ground to a fine powder, owing to their thermoplastic properties. Moreover these particles have the tendency to agglomerate during drying or storage. It is also true that these precipitated polyvinyl acetals contain residues of solvent, acid catalyst and other impurities which are difiicult to remove. These impurities have rendered unstable many products formed from these acetals. It has also been proposed to condense polyvinyl alcohols with aldehydes in the presence of a minimum quantity of water but here again diiiiculties have arisen from the tendency of the condensate to form lumps and a separate precipitation step has been required.

We have discovered what we believe to be the 2 first practical one-step method of preparing poly vinyl acetals of any type directly in the form of very fine particles without the necessity of a subsequent precipitation step. We also appear to be the first to have discovered a method of producing polyvinyl aromatic acetals in the form of substantially uniform fine particles whose average size is as low as 4 microns or below. More specifically We believe that we are the first to have described a method of preparing polyvinyl acetals, containing acetal groups derived from aldehydes of the benzene and naphthalene series, in which the polyvinyl acetals are precipitated in the form of extremely fine particles as fast as they are formed and without the necessity for any subsequent precipitation step. The precipitated products thus obtained are highly pure, stable, free from acid residues and, unexpectedly, they can be dyed directly in extremely bright and fast colors. Aliphatic polyvinyl acetals cannot be dyed in this manner since they have poor aifinity for dyestuffs and their particles would coalesce if dyed warm.

- The dyed particles produced in our process are so finely divided, having a maximiun particle size not exceeding 20 microns and an average particle size usually within the limits of 1.5 and 4 microns, and are so brilliantly dyed that they can be used directly as pigments for incorporaticn into paints, varnishes, printing compositions, coating media, plastics and the like. It is also possible to utilize the dyed particles directly as molding powders since they can be molded under the application of heat and pressure. Our discoveries thus make it possible for the first time to produce brilliantly colored and stable organic pigments which cover the entire color range, all having the same brightness and fastness toward light and all on the same substratum. These products are truly pigments and molding powders in one and give products of perfect evenness and extreme brightness of colors. Our process of producing these products is both simple and practical. A dilute aqueous solution containing from about 1 to 20 per cent by weight of a polyvinyl alcohol is first prepared. The polyvinyl alcohol in this solution is then condensed with an aldehyde of the benzene and naphthalene series which is in a highly-dispersed state in the presence of an acetalizing catalyst and at a temperature within the range of from about 1 to 80 0. usually under conditions of agitation, followed by recovery of the finelydivided acetal which is thereby precipitated.

The aqueous polyvinyl alcohol solution used in this process must have a low viscosity and, in the aeessoa case of high-viscosity alcohols, the maximum concentration which can be used is about per cent by weight. Low-viscosity commercial prodnets are available, however, which can be used in concentrations as high as per cent by weight. The alcohol used can be of the so-called partial type.

Partial polyvinyl alcohols are produced by partial hydrolysis of polyvinyl esters and contain residual ester groups, usually acetyl groups. During the hydrolysis reaction the products become gradually more soluble in water as the ester groups are replaced by hydroxyl groups. We have found that the hydrolysis must be continued until at least about 80 per cent of the original ester groups have been replaced with hydroxyl groups. In other words the polyvinyl alcohols which are suitable for use in our process must contain no more than about 20 per cent of residual ester groups. The alcohols must also be water soluble, at temperatures within the range indicated above, in the amount of at least about one per cent by weight. The polyvinyl alcohol may also contain aliphatic acetal groups in lieu of or in addition to ester groups. These aliphatic acetal groups may be derived, for example, by partial acetalization of a polyvinyl alcohol or of a partial polyvinyl alcohol, using an aliphatic aldehyde, It is also possible to acetali'ze a polyvinyl alcohol more or less completely and then partially hydrolyze the product to obtain a partial polyvinyl acetal or esteracetal, containing free hydroxyl groups. Pure polyvinyl alcohols can be used in our process but the commercial product, which usually contains up to 5 per cent of residual ester groups, is just as satisfactory and much cheaper.

We have found that in order for partial polyvinyl acetals or acetal-esters to be useful in our process they must contain at least about 35 per cent of free hydroxyl groups, that is 35 per cent of the hydroxyl groups which would theoretically be present in the unsubstituted alcohol. Moreover we have found that no more than about 20 per cent of the hydroxyl groups of the unsubstituted polyvinyl alcohol can be esterified and no more than about 50 per cent can be acetalized with aliphatic acetal groups. These figures apply particularly to low molecular aliphatic ester and acetal groups.

The aromatic aldehydes used in the condensation step of our process can be of widely different type. Any aryl or aralkyl aldehyde is operative and these aldehydes may be substituted, the only restrictions being that the aldehyde is stable under the conditions of the reaction, that the aldehyde group is the chief function or the group which is preferentially reactive with alcohol groups of the polyvinyl alcohol, and that they be free or substantially free from hydroph-illic groups, such as hydroxyl, sulfonic, carboxyl and amino so they will be insoluble in water. Among the more useful of. these aldehydes there may be mentioned benzaldehyde, substitution products thereof, such as halo-benzaldehydes, such as chloro-benzaldehydes and iiuoro-benzaldehydes; homologues, such as tolualdehydes; nitrobenzaldehydes, alkoxybenzaldehydes, naphthalclehycles and the corresponding substitution products .of naphthaldehydes.

The following specific aldehydes, aside from benzaldehyde, have been tested .by .us and found satisfactory:

(a) .Hornologues: .p-tolualdehyde.

lb) Halogen derivatives: ,o,. mand p-mono- 4 chlorobenzaldehydes; oand p-monofluoro-benz aldehydes; 2.4-, 2.5- and 2.6-dichloro-benzaldehydes; 2.4.5-trichlorobenzaldehyde.

(c) Nitro-derivatives: m-nitro-benzaldehyde; p-nitro-benzalclehyde (in mixture with benzaldehyde).

(d) AlkoXy-derivatives: oand p-methoxybenzaldehydes; o-ethoxy-benzaldehyde.

' e) Aldehyde grou in side chain: phenyl acetaldehyde, cinnamic aldehyde.

(1) Naphthalene derivatives: Z-naphthaldehyde, l-naphthaldehyde and fi-bromo-l-naphthaldehyde.

The aliphatic acetal groups in our polyvinyl aromatic acetals can be derived from such diverse aldehydes as formaldehyde, butyraldehyde and stearaldehyde. These groups are of relatively minor importance as compared to the aromatic acetal groups. Any aliphatic aldehyde in which the aldehyde groups is the chief function can be used to supply these aliphatic acetal groups.

As indicated previously the condensation step of our process should be conducted at temperatures not substantially above C. and, of course, many of the aromatic aldehydes falling within the above definition are solids at these temperatures. This necessitates the use of some method of dispersing these solids in the aqueous polyvinyl alcohol. Several methods known per so are available for this purpose. One of the most advantageous is to dissolve the solid aldehyde in an inert organic solvent and then to add the result.- ing solution to the polyvinyl alcohol under con ditions of agitation. The solvents used must be of the type in which the resulting polyvinyl aromatic acetals are insoluble since otherwise the acetals will tend to be gelatinous when formed rather than precipitating in finely-divided form. Low molecular alcohols, such as ethyl and propyl alcohols can be used as solvents, for example, since small proportions of these in the reaction medium do not interfere with the precipitation of the polyvinyl aromatic acetate. Glycerol and ethylene glycol can also be used in some cases since these do not interfere when present in the reaction medium. But this medium must be kept substantially free from organic solvents for the polyvinyl aromatic acetals.

One of the most satisfactory methods we have discovered for utilizing solid aldehydes in our process is to dissolve them in benzaldehyde or other liquid aliphatic or aromatic aldehyde and then to add the resulting solutions to the aqueous polyvinyl alcohol solution. In this way mixed polyvinyl acetals are produced. If mixed acetals are not desired it is possible to form aqueous emulsions or dispersions of the solid aldehydes by use of the so-called colloid mill, for example, and then to use these in the process. It is only necessary that the aromatic aldehyde be finely dispersed in the reaction medium and any method of accomplishing this result can be used.

Any acetalizing catalyst can be used to produce the desired condensation between the aromatic aldehyde and polyvinyl alcohol. Many of these are known and it is within the skill of the art to select one which is suitable. Among those which have been found particularly suitable are strong acids, such as hydrochloric, sulfuric, phosphoric, oxalic, tartaric, chloroacetio, lactic, benzene sulfonic and naphthalene sulfonic acids. Any acid or acid salt which is capable of producing acidities within the pH range of from about 1.5 to 2.6 is satisfactory. Other known acetalizing catalysts, such as calcium chloride, zinc chloride, ferric chloride and boron trifluoride are operative.

The conditions under which the condensation reaction is conducted may be varied. As indicated previously the best temperature range is from about 1 to 80 C. but any temperature above the freezing point of the reaction mixture and at least about 20 C. below the softening points of the reaction products can be utilized. Temperatures should be avoided which cause the aldehyde to become appreciably soluble in the reaction mixture. Conditions should be selected such that the polyvinyl aromatic acetal formed in the process is so highly insoluble in the re- 1 action medium that it will precipitate as fast as it is formed in the form of extremely fine particles. Agitation promotes this result and for that reason is advantageous. We usually employ a stirrer in the reaction zone rotating between 250 and 1200 R. P. M.

The time of the reaction is not critical. It is merely necessary to continue the reaction until it is substantially complete. This usually requires from about 1 to 4 hours, depending upon the acidity of the reaction medium, the concentrations of reactants, the temperature employed and the particular reactants. These factors are largely interdependent and it is possible to obtain equally satisfactory results using different sets of conditions. For example it is possible to prepare substantially identical products by carrying out the reaction at 60 C. for one hour at a pH of 2.6, or at 30 C. for 4 hours at a pH of 1.63 or at 1 C. for 4 hours at a pH of 0.76, the proportions of aromatic aldehyde to polyvinyl alcohol remaining the same in all cases.

It is usually advantageous to have a compatible emulsifying agent present in the reaction zone in order to assist in keeping the aldehyde in finely divided form. Any emulsifying agent can be employed which is stable under the conditions of the reaction, i. e. which is stable in acid solution, and non-reactive with the reactants. A large number of surface active agents are known which meet these requirements. Most of these are of the so-called anionic type. The organic sulfonates and sulfates falling within this category when dissolved in water usually produce acid solutions and many of these are sufiiciently 7 acid to serve simultaneously as acetalizing catalysts. The so-called non-ionic surface active agents such as the polyglycol ester of cocoanut oil fatty acids or polyglycol mono-oleate, are also suitable provided that they are stable under the conditions of reaction or provided that they form reaction products during the process which have emulsifying properties. Among the other suitable surface active agents there may be mentioned sodium lauryl sulfate and sodium oleyl sulfate; alkali metal salts of sulfonated esters or amides of higher fatty acids, such as the sodium salt of the N-methyl tauride of oleic acid; or salts of sulfonated aliphatic dicarboxylic acid esters, such as the dioctyl ester of sodium sulfosuccinic acid. A long list of suitable surface active agents fulfilling the listed requirements can be found in the pamphlet entitled Synthetic Organic Chemicals, United States Production and Sales of Surface-Active Agents, 1948, published by the U. S. Tariff Commission.

Our process can be conducted in various ways. Thus it is possible merely to add the aromatic aldehyde to the aqueous solution of polyvinyl alcohol while stirring the latter. In this case it is desirable to have a surface active agent present either in the polyvinyl alcohol solution or in the aldehyde in order to be certain that the aldehyde is emulsified as it is added. It is also possible to form an aqueous emulsion of the aldehyde and then add this to the polyvinyl alcohol, or to use the reverse procedure of adding the alcohol solution to the aldehyde emulsion. The catalyst can be added either before or after the mixing step.

By suitable changes in procedure the particle size of our polyvinyl aromatic acetals can be closely controlled. It is possible, for example, to obtain products having an average particle size of from 8 to 10 microns with none over microns or in the other extreme to obtain products having an average particle size below one micron and impossible to measure by ordinary methods. Such products do not settle out of the reaction mixture but remain suspended indefinitely. The most useful products have particles between about 0.5 and 4 microns in diameter.

An unexpected result obtained in our process is that our products have particle sizes which show astonishing uniformity. Products can be obtained in which up to 90 per cent of the particles are between 1.5 and 3.5 microns, none exceeding 4.5 microns. The frequency distribution of particle size for one of our products showed 65 per cent having a size of 2 microns, per cent having a size of 3 microns and 10 per cent having a size of 4 microns. This appears to be a new result in the art.

The polyvinyl aromatic acetal produced in our process must be insoluble in water at the temperatures used in the process and it must have a. softening point at least about 20 C. below these temperatures. Further we have found that if it is desired to produce a dyed product it is essential that our acetals contain at least 20 per cent of unsubstituted hydroxyl groups, that is, 20 per cent of the groups which would theoretically be present in the unsubstituted alcohol. For certain dyestuffs it is necessary that the free bydroxyl groups of our substantially pure aromatic products be within the range of from 40 to per cent and our best colored products are obtained within this range. However satisfactory results can be obtained when up to "70 per cent hydroxyl groups are present provided that the remainder are substantially all aromatic acetal groups. These proportions are varied somewhat when part of the theoretical hydroxyl groups of the polyvinyl alcohol are substituted with ester groups and/or aliphatic acetal groups. But we have found that our products must contain at least about 15 per cent aromatic acetal groups in order that the products be insoluble in water. These relationships are collected in the following table for products capable of being dyed.

Permissible percentages of substituent groups present in polyvinyl aromatic acetals Ester Aromatic Aliphatic Total Free Groups Acetal Acetal Acetal Hydroxyl Percent Percent Percent Percent Percent It is evident from the above table that in our process the ratio between the aromatic aldehyde and the polyvinyl alcohol used in the process 5 must be controlled so that from to 70 per cent of the hydroxyl groups are replaced by aromatic acetal groups While at least per cent of the hydroxyl groups must remain free. This means that the original polyvinyl alcohol must contain at least per cent of free hydroxyl groups. The proportions of aromatic aldehyde to polyvinyl alcohol required to produce the products whose compositions are represented in the above table cannot be set out in any simple manner. It is, however, a simple matter of experiment to determine the proper proportions to be employed to produce a product of any given analysis within the above table with a given polyvinyl alcohol or perti'alpolyvinyi alcohol, a given aldehyde, and under given reaction conditions. The required proportions can be estimated rather closely from the specific examples which follow. A rough estimate can be gained from the facts that, with a polyvinyl alcohol in which about per cent of the hydroxyl groups are free a molecular ratio of aromatic aldehyde to polyvinyl alcohol of 0.25 to 1 leads to the replacement of about 40 per cent of the available hydroxyl groups by aromatic acetal groups. aldehyde to polyvinyl alcohol of 0.5 to 1 is used, the replacement will be about 69 per cent, while if the molecular ratio is 0.7 to 1 the replacement will be about 7i) per cent. Molecular ratios as high as 0.8 to 1 can be used in some cases. With partial polyvinyl alcohols in which a substantial proportion of the hydroxyl groups is already substituted by ester and/or aliphatic acetal groups, smaller proportions of aromatic aldehyde are required to form insoluble products having the I desired properties. Molecular ratios as low as 0.1 to 1 have been used satisfactorily in such cases. So the over all ratios range from about 0.8 to 1 to 6.1 to 1. To produce products which can be dyed economically it is necessary to use ratios producing water-insoluble polyvinyl aromatic acetals having compositions within the limits set out in the above table. If products are desired which need not be dyed an excess of substitution by aromatic aldehyde over the proportions stated is permissible and products can be obtained which contain substantially no free by droxyl groups.

.Our acetals do not have sharp melting points.

When heated in the dry state they slowly sinter and agglomerate at temperatures ranging from about to C. This softening is very gradual and somewhat variable from sample to sample so that it is difiicult to set a definite softening temperature or range from a given i-.;,

product. The compositions of our acetals within the ranges set out do not have a great efiect upon the softening ranges. Likewise products obtained from diiierent aromatic aldehydes do not possess significantly different softening ranges.

Our finely divided acetals are insoluble in water, ether, petroleum fractions and cyclic hydrocarbons, such as decahydronaphthalene, benzene, toluene and Xylene. l 'hey are insoluble or slightly soluble in aliphatic alcohols such as methyl, ethyl, n-butyl, and n amyl alcohols; in aliphatic ketones, such as acetone, methyl-ethylketone, and methyl-isobutyl lietone; in aliphatic esters, such as ethyl acetate, n-butyl acetate, and ethyl lactate; in chlorinated hydrocarbons, such as trichlorethylene, tetrachlorethane and monochloro-benzene. They are freely soluble in a limited number of solvents belonging to different chemical groups, such as benzyl alcohol, tetrahydrofuriuryl alcohol, diox-ane, m-cresol If a molecular ratio of aromatic 9 aromatic and hydroaromatic amines, such as aniline, mtol'uidine, p irylidine and cycl'oheiryl amine.

lvlixture's of compounds which individually do not dissolve our acetals are in some cases good solvents, e. g. methyl cyclohexanol and benzene or trich-lorethylene and ethyl alcohol.

With increasing replacement of the hydroxyl groups by acetal groups there is a tendency towards greater solubility in organic solvents which becomes particularly marked when approaching 70% replacement.

As indicated previously our polyvinyl aromatic acetals can be dyed satisfactorily with a large range of dyestuffs. By means of an extensive series of tests we have established the fact that our polyvinyl aromatic acetals possess a high aiiinlty for all dyestuu's which are characterised by the presence therein of at least one hydrophillic group selected from the class consisting of amino groups, phenolic hydroxyl groups and enolic hydroxyl groups and by having a solubility in water within the range of from about 0.01 to 1.5 per cent by weight. The amino groups in the dyestuff may be substituted, for example by methyl, ethyl and phenyl groups. We have dis covered that dyestuffs of greater solubility than that stated have a reduced affinity for our arc-'- matic acetal's, which accounts for the solubility limitation. It is possible to have present in the dyestufi molecule water-solubiliz ing' grou s'or an acid character, such as -*-CO'OH and '-'SO'2OH, provided that these groups do not increase the solubility of the dyestuffs above the limit stated. Cther inert substituent groups which do not take part in the reaction can also be present in the dyestuli.

We have made the surprising discovery that our polyvinyl aromatic facetals can be dyed with what are known as basic dyestuffs to produce colors which are not only extremely bright but which also have surprising fastness to light. It is well known, of course, that these dyestuffs as ordinarily applied to fabrics with the aid of tannic acid are extremely bright in shade but that with few exceptions they are fugitive to light. Pigments which are tast to light have been prepared previously by precipitating these dyes with phospho-thngstic, phospho inolybd-ic or similar complex acids but in making such pigments much of the brightness of the original dyestufi" is lost. We therefore believe that our present invention provides for the first time a method of obtaining pigments from basic dyestuffs which are both of maximum brightness and fastness to light. 0111 pigments cover the whole gamut of hues but the pinks, bluish reds, purples and violets are particu'larly valuable because these hues have not heretofore been represented in the desired brightness among the "fast-tO-light pigments available to the trade. The following basic dyestuffs have given excellent results in our tests .Acronol Yellow T (Col. Ind. No. 815).; Tannin Orange R 0901. Ind. No. 72) Rhodamlne B (Col. Incl. No. 749); Magenta (001. Ind. No. 677 Astraphloxine FF (Rowe, Inst. of Chem. Lec tures, 1938, 10; 5:6); Cresyl Blue BBS (Col. Ind. No. 877.) ;.Brilliant Green Y (Col. Ind. No. 662.).

These dyestuffs are dissolved or suspended in water, the polyvinyl acetal is added, and the mixture is kept stirred with or without heating, until the dyestufi base has been taken up. The dyed product istheii washed free from unfixed dye stuff and dried. If the dyestu-ff is stable at a pH between 0.2 and 0.6, it may also be present at the 9 moment of formation of the polyvinyl acetal and the dyed pigment may be obtained in one operaion.

Alternatively, the dyestuff may be added to the reaction medium after the formation of the polyvinyl acetal and dyeing carried out in the same liquor, adjustment bein made to the optimum pH if necessary.

Further useful pigments are obtained from dyestuffs containing one or more basic groups, but not generally known as basic dyestuiis, as for instance: p-amino-azo-benzene; 2 ethoxybenzene-azo-alpha e naphthylamine 1 :4 diaminoanthraquinone; 1:4 dimethylamino anthraquinone. I

Examples of dyestuffs containing hydroxyl groups are: Sudan G (Col. Ind. No. 23) Alizarine Yellow R (Col. Ind. No. 40) Alizarine Bordeaux B paste (Col. Ind. No. 1045).

Examples of dyestuffs containing amino and/or hydroxyl groups and also water-solubilizing roups are: 4-.sulphobenzene-azo 2 hydroxy- 3 -naphthoic acid-beta-naphthylamide; Chrysophenine G (Col. Ind. No. 365); Chlorazol Fast Red FG (Col. Ind. No. 419 suppl.) Chlorazol Fast Helio 2RD; (Col. Ind. No. 319 suppl.) Solway Sky Blue BS (Col. Ind. No. 1088 suppl.) Solway Purple (Col. Ind. No. 1073).

Pigments of outstanding merit, characterized by excellent fastness to light, very good resistance to wet treatment and insolubility in common or ganic solvents are also obtained with dyestuffs belonging to the class known as vat dyestufis, as described more fully and claimed in copending application, filed by the two of us jointly with Ernest Spinner, Serial No. 18,083, filed March 30, 1948, now Patent No. 2,534,136. The vat dyjestuff is applied in the form of a water-soluble alkali salt of its enolic leuco-derivative, which latter possesses a high aflinity for our polyvinyl acetals and after the dyeing operation, the original insoluble dyestufi is regenerated by oxidation. The present claims, of course, do not include the subject matter of the claims of this acknowledged patent.

Vat dyestuffs in their original form have occasionally been used as pigments for application to a variety of materials by means of an ad hesive. When applied in such manner, they mostly yield dull colors of an intensity and brightness generally much inferior to that obtainable from the same dyestuffs when dyed on textile materials in the usual manner. Because of these defects and of the high cost of vat dyestufis generally, their use in the form of pigments has remained very limited.

The invention of No. 2,534,136 provides a process for producing vat color pigments of a new and improved type, in which the qualities of brightness, color yield and fastness are at least equal to those possessed by the same dyestuffs when dyed on textile materials in the usual manner.

These dyestuffs comprise two main groups: (1) indigoid dyestuffs, of which indigo itself, thioindigo, and their halogen, amino, alkyl and alkoxy derivatives are the main representatives and (2) anthraquinonoid dyestuffs which are derived from anthraquinone and other polynuclear quinones, such as benzanthrone, pyranthrone, anthanthrone, dibenzanthrone and the like. Dyestuffs belonging to either of these groups, which fulfill the requirements stated previously are suitable for producing valuable pigments and molding powders according to the invention. Ex-

amples are: Anthra Yellow GC (Rowe, Inst. Chem. Lect. 1938, p. 68); Indanthrene Brilliant Orange GK (Rowe, I. C. L. p. 67) Ciba Scarlet G (Col. Ind. No. 1228); Hydron Pink FF (Rowe, I. C. L. p. '73) Durindone Red BS (Col. Ind. No. 1207) Indanthrene Brilliant Violet Delta R. (Rowe, I. C. L. p. 90) Ciba Blue 23 (C01. Ind. No. 1184); Caledon Jade Green XN (Col. Ind. No. 1101); Ciba Brown G (Col. Ind. No. 1150, suppl. p. 16).

As described in copending application, Serial No. 50,252, filed April 18, 1949, very valuable pigments are also obtained by dyeing the polyvinyl acetal with coupling components suitable for the production of insoluble azo dyestuffs, which coupling components comprise a hydroxyl group attached to an unsaturated carbon-carbon linkage, i. e. the grouping The double bond of this grouping may be part of an aromatic nucleus, such as in phenols and naphthols, or it may be part of a heterocyclic ring, or of an aliphatic chain, as in enolic compounds derived from aceto-acetic acid. All these compounds have a strong affinity for our polyvinyl acetals, and are taken up in substantial amounts from the aqueous solutions of their alkali salts. Preferred compounds are Z-naphthol and the coupling components commercially grouped under the designation of Naphthol AS, which comprises arylamides of aromatic hydroxy-carboxylic acids, such as 2-hydroxy-3-naphthoic acid, and of keto-enolic compounds having one or more groupings RCO-CHzCO-. Examples of coupling components included in the Naphthol AS group are 2-hydroxy-3-naphthoic acid anilide (Naphthol AS), 2-hydroXy-3-naphthoic acid 0- toluidine (Naphthol AS-D), 2-hydroxy-3-naphthoic acid p-anisidide (Naphthol AS-RL), 2- hydroxy-carbazole-3-carboxylic acid-p-chloranilide (Naphthol AS-LB), diacetoacetic acid-otolidide (Naphthol AS-S), and 2-acetoacetylamino 6 ethoxy benzothiazol (Naphthol AS-IAG). Examples of phenolic compounds which yield valuable pigments are the dihydroxydiphenylmethanes, such as 2.2'-dihydroxy-5,5- dimethyl-diphenylmethane.

After the polyvinyl acetal has been dyed with one or more of the above compounds, it is aftertreated with an aqueous solution of a diazonium compound derived from an aromatic amine devoid of wa-ter-solublizing substituents, whereby the insoluble azo dyestuff is formed as described and claimed inSer. No. 50,252. Examples of suitable amines are: aniline, toluidine, benzidine, amino-azo-benzene, amino-diphenylamine, naphthylamine, amino-anthraquinone and substitution products of same such as their halogen-, cyano-, nitro-, alkoxy-, phenoxy-, halogenomethyland benzoylamino derivatives.

All of the above described dyestuffs and dye stuff components have the common properties mentioned above, namely they all have in their molecules at least one hydrophillic group selected from the class consisting of amino groups, phenolic hydroxyl groups and enolic hydroxyl groups and they all have a solubility in water ranging from about 0.01 to 1.5 per cent by weight. These common properties are what make these dyestufis operative in present process which covers the use of these dyestuffs with the exception of the vat dyes of No. 2,534,136 and the azo dyes of Ser. No. 50,252. r

In the dyeing of our polyvinyl aromatic acetals hydroxyl groups.

with vat dyes we have found that best results are obtained in the case of acetals in which the ratio of hydrozzyl groups to acetal and ester groups is within the rather narrow range of from 40:60 to 601%. These dye-stuffs are used within a temperature range at which acetals containing less than about 40 per cent acetal groups would tend to soften and agglomerate, whereas the affinity of our acetals for these dyestuiis decreases so greatly when the acetal group content exceeds 60 per cent that dyeing with these dyestuffs is no longer economical. But in the case of basic dyes and other dyes which can be used at low temperatures the affinity of the acetals for the dyestuffs is reasonably good even when the acetal groups reach from '70 to '75 per cent of those theoretically possible and, at the low temperatures which are feasible, acetals can be used which contain only about to per cent of the aromatic acetal groups would be theoretically possible.

The following specific examples represent'operating embodiments of our process which have been found satisfactory in actual practice.

Example 1 43 grams of polyvinyl alcohol (containing 5% unhydrolyzed acetyl groups) are dissolved in 390 mls. of water, 1.7 grams of sulphuric. acid. in mls. of water are added, and 41 grams of benzaldehyde, previously emulsified in a solution of 2 grams sodiurn-dioctyl-sulphosuccinate in mls. of water, is stirred in. The mixture has a pI-I of 1.77. It it heated to 60-70 (3., and kept at this temperature for 1 hour under stirring at a speed of 11.00 revolutions per minute. The re- Suiting; product is then filtered, washed with dilute. ammonia. to remove unreacted benzaldehyde and dried. The dry product is a white impalpable powder, whose composition is that of. a partial polyvinyl henzal which 48.5% of the hydroxyl groups remain. unreacted. Its particle size. does not exceed 7 microns, and is about 3 microns in 70% of the product.

If in the above preparation. 5.6 grams of sodium oleyl sulphate are used as the emulsifying agent in place of sodium di-octyl-sulpho-succinate, a similar product is obtained.

Example 2 38 grams of the same polyvinyl alcohol are dissolved in 627 mls. of water, 2 grams sulphuric acid in 14:1 mls. of water are added and an emulsion of 2". of benzaldehyde in 170 mls. of a 2% aqueous solution of sodium dioctyl-sulplwsuccinate is stirred in. The mixture, which has a pH of 1.72 is further stirred. for 4- hours at 6., at a speed of about 1000 revolutions per minute. Th8 polyvinyl benzal which has formed is then filtered, washed with hot dilute sodium bisulphite solution and subsequently with hot water toremove unreacted benzaldehycle and dried. The product is a partial polyvinyl benzal possessing about of unreacted hydroxyl groups, in which the particle size is between 1.5 and 3.5 microns in 90% of product.

If in the above preparation only 19 grams of benzald'ehyde are used instead of 2'7 the resulting partial polyvinyl henaal possesses about of unreacted hydroxyl groups. If on the contrary 38 grams of benzaldehyde are used, a product is obtained which only contains about 40% of free In both cases, the product is similar to the preceding in fineness.

tin

Emmple 3 40 grams of the same polyvinyl alcohol are dissolved in 110 mls. of water, 2 grams of oxalic acid and 12 grams of paraldehyde are added to the solution. and the whole is heated under a reflux condenser to C. for 1 hour and then cooled. ihe product consists of a partial polyvinyl alcohol soluble in cold water but insoluble hot water, in which 5% of the hydroxyl groups have been replaced. by acetal groups and 50% by ethylidene groups. The product is diluted with 771 mls. of Water and 20 grams of bensaldehyde, previously emulsified in l5 grams of a 2% by weight solution or sodium dioctyl-sulpho-succinate, are added. The mixture, which has a pH of 1.68 is vigorously stirred for 2 hours at 20 C., whereby a finely divided polyvinyl benzal is obtained which is filtered off, washed with dilute ammonia and dried. Approximately of the hydroxyl groups have been replaced by acetyl groups. 50% by ethylidene groups and 25% by benzylidene groups.

Example 4 50 grams of polyvinyl alcohol are dissolved in 950 mls. of water, 10 mls. of 20% by weight sulphuric acid emulsion of '70 grams 0- chloro-benzaldehyde in 112.5 mls. of a 2% by weight solution of sodium dioctyl-sulphosuccinate are added, and the mixture is vigorously stirred for 1 hour at a temperature of C. The product is filtered and washed and after drying is a fine, impalpable powder.

Example 5 If in the preceding example grams of 2- naphthaidehyde are used instead of o-chlorobenzaldehyde, a similar product is obtained.

Example 6 2i) grams of polyvinyl alcohol are dissolved in 2 liters of water, 25 mls. of 10% by weight sulphuric acid and an emulsion of 20 grams of benzaldehyde in mls. of a 2% by weight solution of sodium dioctyl-sulphosuccinate are added, and. the mixture, which has a pH of 1.63 is vigorously stirred for 4 hours at 30 C. after which the product is filtered, washed. and dried.- The product is a very fine white powder having an average particle size of 4 microns.

Instead of sodium dioctyl-sulpho-succinate, the same amount of the sodium salt of oleyl-methyltaurine may be used as the emulsifying agent.

Example 7 If in the preceding example the polyvinyl alcohol is dissolved in 390 mls. of water and only 6 mls. of 10% by weight sulphuric acid are added, the resulting product is so fine that it does not settle out in the reaction mixture but remains in suspension indefinitely.

Example 8 20 grams of polyvinyl alcohol are dissolved in 354 mls. of water, a solution of 1.3 grams of oxalic acid in 26 mls. or water is added and an emulsion of 20 grams benzaldehyde in mls. of a 2% by weight solution of sodium dioctylsulpho-succinate is stirred in. The mixture, which has a pH of 1.89, is vigorously stirred for 4 hours at 30 C., after which the product is filtered, washed and dried.

Instead of oxalic acid, 14 grams of 70% lactic acid may be used. The pH of the mixture is? 13 1.97 in this case. The productsobtained are similar to that of Example 2.

Example 9 40 grams of polyvinyl alcohol are dissolved in 695 mls. of water at 55 C. and 25 mls. of by weight sulphuric acid are added. 40 grams of p-chlorobenzaldehyde is emulsified at 55 C. in 40 mls. of a 2% aqueous solution of sodium dioctyl-sulpho-succinate and added under stirring to the first solution. The mixture is then stirred at 55-60 C. for 2 hours. The resulting polyvinyl p-chlorobenzal precipitates in the form of an extremely fine powder.

If the p-chloro-benzaldehyde is replaced by 50 grams of 2,5-dichloro-benzaldehyde and the reaction is carried out for 2 hours at '70-'75 C. a similar product is obtained. The 2.4- and 2.6- dichlorobenzaldehyde and 2.4.5-trich1orobenzaldehyde may also be used in equivalent amounts.

Example 10 40 grams of polyvinyl alcohol are dissolved in 727 mls. of water, 25 mls. of 10% by weight sulphuric acid and an emulsion of 48 grams of ofluoro-benzaldehyde in 160 mls. of a 2% aqueous solution of sodium dioctyl-sulpho-succinate are added. The mixture is heated under vigorous stirring at 40 C. [for 3 hours and precipitation of the polyvinyl-o-fluoro-benzal is completed by further stirring at C. for 16 hours. A product of average particle size about 3 microns is obtained.

Example 11 40 grams of polyvinyl alcohol are dissolved in 1060 mls. of water and mls. of 10% by weight sulphuric acid is added. 40.2 grams of p-nitrobenzaldehyde is dissolved in 10 grams of benzaldehyde by warming and the mixture is emulsified in 140 mls. of a 2% aqueous solution of sodium-dioctyl-sulpho-succinate. The emulsion is then stirred into the polyvinyl alcohol solution heated to 60 C. and the mixture is reacted at that temperature for 4 hours, yielding a finely divided product.

Example 12 The acidified polyvinyl alcohol solution of the preceding example is mixed with an emulsion of 45.5 grams of p-tolualdehyde in 140 mls. of a 2% aqueous solution of sodium dioctyl-sulphosuccinate and the mixture is reacted at 60 C. for one hour, yielding an extremely fine product.

Example 13 The tolualdehyde of the preceding example may be replaced by 51.3 grams of 0- or p-methoxy-benzaldehyde with similar results.

Example 14 The tolualdehyde may also be replaced by 50 grams of either phenyl-acetaldehyde or cinnarnic aldehyde but the reaction is then carried out at C. for 4 hours.

Example 15 20 grams of a polyvinyl alcohol (containing 3.4% of residual acetyl groups) are dissolved in.

380 mls. of water and 4 mls. of 10% by weight sulphuric acid are added. The mixture is heated to 70 C., 2 grams of paraldehyde are added under vigorous stirring and allowed to react at that temperature for 30 minutes and then cooled down to 20 C. during a further 30 minutes. 15

grams of benzaldehyde. previously emulsified in 20 mls. ofa 2% aqueous solution of sodium dioctyl-sulpho-succinate are added under. vigorous stirring to the still water-soluble intermediate product and are allowed to react for 4 hours at 20 C. while stirring is continued. The pH of the reaction mixture is 1.82. The partial polyvinyl benzal which has formed is then filtered and washed. The product, which contains about 20% of the hydroxyl groups replaced by ethylidene groups and 30% by benzylidene groups, is a fine, impalpable powder of average particle size of 2.6 microns.

Example 16 20 grams of a partial polyvinyl alcohol containing 20% residual acetyl groups are dissolved in 180 mls. of water, 8 mls. of 10% by weight sulphuric acid are added, and the mixture is heated to C. 6.5 grams of paraldehyde are then introduced under vigorous stirring and, allowed to react for 30 minutes at 50 C. and allowed to cool down to 30 C. The intermediate product is still water-soluble at that temperature. Excess acetalclehyde is then removed by bubbling air through the solution for one hour, 245 mls. of water and 11.3 mls. of 10% by weight sulphuric acid are added and 14 grams of benzaldehyde previously emulsified in mls. of a 2% solution of sodium dioctyl-sulpho--succinate are stirred in and allowed to react at 30 C. for a hours under vigorous stirring. The pH of the reaction mixture is 1.41. The product is a fine powder and contains about 20% of the hydroxyl groups replaced by acetyl groups, 30% by ethyli dene groups and 30% by benzylidene groups.

Example 17 10 grams of polyvinyl alcohol are dissolved in 230 mls. of water at 60 C. 7.5 grams of 5-bromo-l-naphthaldehyde are dissolved in 4.5 grams of benzaldehyde and the solution is emulsified in 60 mls. of a 2% solution of sodium-dioctyl-sule pho-succinate at 60 C. under vigorous stirring.

The emulsion is then mixed with the solution of polyvinyl alcohol and 6.25 mls. of 10% by weight sulphuric acid are stirred in gradually over one hour. Stirring is contnued for another hours at 60 C. to complete the precipitation of the polyvinyl 5-bromo-1-naphthol, which is obtained as a very fine powder.

Example 18 20 grams of a partial polyvinyl alcohol containing 20% of residual acetyl groups are dissolved in mls. of water, 20 grams of 37.5%-

by weight formaldehyde and 8 mls. of 10% by weight sulphuric acid are added and the mixture is heated to 70 C., reacted at that temperature for 2 hours under stirring and cooled. The still water-soluble intermediate product is then diluted with 280 mls. of water, 8.4 mls. of 10% sulphuric acid are added and 11.2 grams of benzaldehyde previously emulsified in mls. of a 2% solution of sodium dioctyl-sulpho-suc cinate are stirred in. The mixture is allowed to react under vigorous stirring at 20 C. for 4 hours; after which the product is filtered, washed and dried. The product is a very fine powder in which about 20% of the hydroxyl groups are substituted by acetyl, about 22% by methylene and about 28% by benzylidene groups.

If in the first part of the above preparation, 6.5 grams of n-butyraldehyde is used instead of formaldehyde and the mixture is heated to 50 C., the reaction takes place very rapidlyand is i5 already completed after 5 minutes; The result ing gel re'dissolv'es on. cooling and is then reacted with benzaldehyde as described above; In the resulting product about 20% of the" hydroxyl groups are substituted by acetyl, about 21% by butylidene' and: about 34 by'benzylidene group's.

Example 1 9 14 grams of polyvinyl alcohol containing 5% of residual acetyl groups are dissolved in 126 mls. of water, the solution is heated to 70 C.- and grams of stearaldehyde are dispersed: in it. 6 mls. of 10% by weight sulphuric acid are then added and the mixture is reacted under stirring for one" hour at 70 C. The resulting intermediate: product is then diluted with 185 rule. at water, and further reacted with benzaldehyd-e' as described in the preceding example. The product is a partial polyvinyl stearalbenzal, in the form. of very fine. white powder.

Example 10 grams of the partial. polyvinyl alcohol used in Example 3.8 is dissolved. in 210 mls. of water and 7.6 5 mls. of 10% by weight sulphuric acid are added to the solution. An emulsion of 4 grams of n heptaldehyde and 10 grams of benzaldehyde in 90 mls. of a 2% solution of sodium dioctyl-sulpho-succinate is then stirred in and the mixture is heated under vigorous stirring for 2. hours at 50 C. The resulting partial polyvinyl heptal-benzal precipitates as a very fine powder.

Instead of n-heptaldehyde, other aliphatic al dehydes such as paraldehyde or butyraldehyde may be used simultaneously with the aromatic aldehyde to produce mixed polyvinyl benzals in finelydivided form.

Example 21 1 00 grams of the dried product formed in 1 are dispersed in a solution of 3 grams Rhodamine B (Color Index No. 749) in 1000 mls. of water. The temperature is raised to 95 C.

and maintained there for 1 hour, the mixture being continually stirred. The product, after filtering and. drying consists of a bright bluishred powder of very good fastness to light.

Example 22 100 grams of the product of Example 3 are dispersed in a solution oi"- 3 grams Brilliant Green Y (Color Index No. 662) in 100 mls. of water. The temperature is raised to 70 C. and maintained there for 1' hour with continual stirring.

The product, after filtering, washing and drying consists of a bright green powder of very good fastness to light.

Example 23 250 grams of a partial polyvinyl alcohol, in which 15% of the hydroxy groups are replaced by acetyl groups and by ethylidene groups and which has been obtained by the partial hydrolysis of. a polyvinyl acetal in which 30% of the hydroxy groups have been replaced by acetyl groups and 70% by ethylidene groups are dissolved in i850 mls. of water containing 10 grams of Rhodamine B (Color Index No. 749) and 562 mls. of a 2% by weight solution of sodium dioctyl-sulpho-succinate added. 125 grams of benzaldehyde are emulsified in the mixture by rapid stirring, 100 mls. of 10% by weight sulphuric acid added and the while stirred at a speed 02 1100 revolutions per minute for 4 hours at a; temperature of 20? C. The product, after filtering, washing and drying consists of a bright bluish-red powder of very good fastness to light.

Example 24 The preparation is carried out as in Example 23, but the Rhodamine B is omitted; in this case a white powder is obtained. 100 grams of this product are suspended in 1000 mls. of a 0.3% by Weight aqueous dispersion of 1:4 di-amino-am thraquinone, the temperature raised to 70 C. and maintained there for 1 hour with continual stirring. The product, after filtering, washing and drying consists of a bright red-violet powder;-

Example 25 100 grams of the product prepared according to Example i are suspended. in a solution of 3 grams Chlorazol Fast-Helio 211K (Color Index No; 319 suppl.) in 1000 mls. of water the temperature raised to it C. and. maintained there for 1 hour with continual stirring. The product, after filtering, washing and drying consists of a reddishvi'olet powder.

Example 26 100 grams of the product prepared according to Example 5 are suspended in a dispersion of 3 grams Sudan G (Color Index No. 23) in 1000 mls. of water, the temperature raised to 50 C. and maintained there for 1 hour with continual stirring. The product, after filtering, washing and drying consists of an orange-yellow powder.

Example 27 10 g. of Indanthrene Brilliant Violet 4R 30% paste (Rowe. 1. 0. page are mixed first with 45 ml. of a 0.4% solution of sodium oleyl sulphate, thenwith 40' ml. of a 33% solution of sodium hydroxide and about 400 ml. of water are added. The mixture is heated to 60 C. and 5 of sodium hydrosulphite, are dissolved in it. When reduction is complete, the solution is made up to 600 ml. with water.

30 g. of a partial. polyvinyl benzal prepared as described in Example 2 and possessing about 50% of unreacted hydroxyl groups are carefully pasted with about 4.5 ml. of the solution of leuco-vat dyestuff, the remainder of the solution is gradually added, the liquor is quickly heated to 60 C. and then gradually over a period of 30 min. to 90 C. and kept at that temperature for a further 30 minutes under continuous stirring. The dyed polyvinyl benzal is then filtered oii, washed twice in succession with 15 ml. of cold water on the filter, then transferred into a shallow vessel with as large a surface as possible exposed to the atmosphere and left for about 16 hours. The oxidation is then completed by stirring the powder with 210 mls. of a 5% solution of acetic acid and allowing to stand for another 15 minutes. The pigment is then filtered off and washed free from acid. It is then further washed at C. with one liter of a solution containing 2 grams of soap, 1 gram of sodium carbonate and 1 gram of sodium percarbonate for 30 minutes, filtered off, washed free from sodium carbonate and dried.

The product is a deep purple powder of outstanding brightness and of excellent fastness to light. The original dyestuff in powder form is a dull purplish black, devoid of any value as a pigment.

Example 28 18 g. of Hydron Pink FF powder (Rowe, l. c. p. 73) are mixed first with 45 ml. of a 10% solution of sodium ricinoleate, then with 60 ml oi a 33% sodium hydroxide solution and about 400 ml. of water are added. The mixture is heated to 80 C. and 18 g. of sodium hydrosulphate are dissolved in it. When reduction is complete, the solution is made up with water to 600 ml.

30 grams of a partial polyvinyl benzal prepared as described in Example 2 and in which about 60% of the alcoholic hydroxyl groups are free, is pasted up and dyed as described in Example 27. Under these conditions, about 85% of the dyestuff in solution is taken up by the par tial polyvinyl benzal.

The liquor is then cooled to 70 C. and kept at that temperature for 15 minutes before filtering. The subsequent procedure is as described in Example 27.

The product is a red powder of a bluer and considerably brighter shade than the original dyestufi. It possesses excellent fastness to light.

Example 29 45 g. of Caledon Jade Green XN 60% paste (Col. Ind. No. 1101) are mixed first with 45 ml. of a solution of sodium sulphoricinoleate, then with 40 ml. of a 33% solution of sodium hydroxide and about 4.00 ml. of water are added. The mixture is then heated to 50 C. and 30 g. of sodium hydrosulphite are dissolved in it. When reduction is complete the solution is made up with water to 600 ml.

30 grams of a partial polyvinyl alcohol prepared as described in Example 2, and in which about 40% of the alcoholic hydroxyl groups are free, are carefully pasted with about 50 m1. of the solution of the leuco vat dyestuff, the remainder of the solution is stirred into the paste and the dyeing is carried out at 90 C. for 30 minutes under stirring.

The liquor is then cooled to 70 C. and maintained at that temperature for minutes before filtering. The subsequent procedure is the same as for Example 27. The product is a green powder of outsanding brightness and excellent fastness to light.

Example 30 28.8 grams of Z-naphthol are dissolved in a mixture of 63 ml. of a 33% solution of sodium hydroxide, 15 ml. of a 25% solution of sodium ricinoleate and 320 ml. of water and the whole then made up to 500 ml. 25 grams of a partial polyvinyl benzal containing about 60% of free hydroxyl groups are pasted with 80 ml. of the above solution and the remainder of the solution is stirred in gradually. The mixture is then heated to 60 C. and kept at this temperature for 30 minutes with stirring after which the polyvinyl benzal is filtered, washed with water and pressed.

9 grams of 4nitro-2-methoxy-aniline are diazotized in the usual manner with sodium nitrite and hydrochloric acid and after adding suificient sodium acetate to neutralize the excess of hydrochloric acid the solution is made up to 300 ml. of cold water. The polyvinyl benzal which has been treated as described in the first part of this example, is now pasted with 80 ml. of the diazonium solution, the remainder of the solution is added gradually and the mixture stirred for about 2 hours. The dyed polyvinyl benzal is then filtered, washed free from diazonium solution with cold water, treated with a solution of 2 grams of soap and 0.5 gram of sodium carbonate per liter for 10 minutes at 95 0., again filtered. washed free of alkali and dried. The

18 product is a bluish red pigment of good fastness to light.

Exampl 31 26.3 grams of 2-hydroxy-3-naphthdic acid anilide are pasted with 15 m1. of a 25% solution of sodium sulphoricinoleate; 45 ml. of a 33% solution of sodium hydroxide and about 400 ml. of hot water are added and after the naphthol has dissolved, the solution is made up with water to 500 ml. 25 grams of a partial polyvinyl benzal containing about 50% of free hydroxyl groups are pasted with ml. of the above solution and the remainder is added gradually. The mixture is then heated to C. and kept at this temperature for 30 minutes with stirring, after which the temperature is allowed to drop to 50 0., when the polyvinyl benzal is filtered, washed with water and hydro-extracted. It is then treated in a diazonium solution obtained in the usual manner from 2.5-diethoxy-4-benzoyl aminoaniline.

The resulting product is a pigment colored blue, which is very much brighter than the azo compound obtained directly in aqueous solution from these components and this advantage is rendered particularly evident when the latter is mixed with some white pigment so as to make it more comparable in depth of shade with the dyed polyvinyl benzal.

If diazotized 2-methoxy-5-methyl-4-benzoylaminoaniline, a bright violet pigment is obtained which shows the same advantage of much superior brightness against the azo compound obtained directly in aqueous solution from these components.

Example 32 28.5 grams of di-aeeto acetic acid-o-tolidide are pasted with 15 ml. of a 25% solution of sodium sulphoricinoleate and 63 ml. of a 33% solution of sodium hydroxide, about 400 ml. of hot water are added and the resulting solution is made up to 500 ml. 25 grams of the partial polyvinyl benzal used in the preceding example are pasted with 80 ml. of the above solution, the remainder being added gradually and then treated for 30 minutes at 90 C. under stirring. The liquor is allowed to cool to 70 C. The treated powder is then filtered, washed with cold water and pressed. It is then further treated with a diazonium solution prepared in known manner from 2-methoxy-aniline. Th product is a lemon yellow pigment of very good fastness to light.

Eatample 33 35 grams of an equimoleeular mixture of 2- hydroxy 3 naphthoic acid anilide and the sodium derivative of 2.5-dichlorobenzene diazonium hydroxide are pasted with 20 ml. of a 25% solution of sodium sulphoricinoleate and 63 ml. of a 33% solution of sodium hydroxide; about 400 ml. of hot water are added and. after the product has dissolved, the solution is made up to 500 ml.; 25 grams of the partial polyvinyl benzal used in the preceding examples are pasted with 80 ml. of the solution and the remainder is stirred in gradually. The mixture is then treated for 30 minutes at 60 C. under stirring. The treated polyvinyl benzal is then filtered, washed with cold water, pressed and then treated with an excess of hot 10% formic acid under stirring. After 10 minutes the dyed polyvinyl. benzal is filtered, washed well with water, treated with hot alkaline soap solution as in the previous exprepared in the usual manner.

19 amples, filtered, pressed and dried. Theproduct is a bright scarlet pigment of very good -fastness to light.

Example 3.4

28.5 grams of 2.2-di hydroxy 5.5'-.dimethyldiphenylmethane are pasted with 56-mls. of a 33% solution of sodium hydroxide about 350 mls. of hot water are added and the resultingsolution made up to 500 mls. grams of a finely divided partial polyvinyl benzal in which the percentage of hydroxyl groups replaced by benzal groups does not exceed are pasted with mls. of the above solution, the remainder being then added gradually and then treated for 30 minutes at C. with stirring. The liquor is then-allowed to cool with continued stirring to 50 C., the dyed powder is filtered off, washed with cold water and drained. It is then treated with a solution of diazotized 2.5-dichlor'aniline The subsequent procedure is the same as in Example 30. The product is an orange pigment of very good fastness to light.

Example 3'5 A partial polyvinyl .benzal prepared as described in Example .1, is molded in a hot press at a temperature of .C. and a pressure of 2 tons/sq. in., for 10 minutes. The resultisa pale yellow, transparent, .fairly hard but resilient molding.

Example 36 A red partial polyvinyl benzal pigment prepared as described in Example 21, is completely a mixed with an equal quantity of a green partial polyvinyl benzal pigment prepared as described in Example 22 and the mixture is molded as in Example 35. The result is a partly opaque molding showing a red, green and black marbled effect.

Example 37 An intimate mixture of equal parts by weight of a partial .polyvinyl benzal prepared as described in Example '1 and a =finepo1y-methylmethacrylate resin powder is molded under the conditions described in Example 35. The result is a pale yellow, translucent product, which is harder than the resin itself.

Example 3'8 50 parts by weight of a partial polyvinyl benzal prepared as described in Example 1, 25 parts by weight of triacetine and25 parts by weight of benzyl alcohol are intimately mixed and then molded at a temperature of 95 C. and a pressure of 3 tons/sq. in., for 2minutes. The result isa flexible transparent rubber-like body of good elastic recovery.

v Example 40.

25 grams of a finely divided'partial polyvinyl benzal are dyed'with 500 ml's. of a solution containing "0.57 grams of 2-hydroxy-3-naphthoic poly-methyl-methacrylate 20 acid-p-an'isidide, 15 grams of sodium hydroxide and 3.75 grams of sodium sulphoricinoleate as described in previous examples. The dyed powder is then treated with a solution of diazotized 5-nitro-2-amino-toluene and the subsequent procedure is'the same as in'Example 30. The resulting pale pink powder is molded in a press at C. and a pressure of 2 tons per square inch. The resulting molding is deep-red.

While we have described what we consider to be the best embodiments of our process it is evident, of course, that various modifications can be made in the specific procedures which have been described without departing iromthe purview of this invention. As indicated previously, in the making of our mixed aliphaticaromat'ic acetals it is possible to condense the polyvinyl alcohol with'the aliphatic aldehyde first to produce a partial polyvinyl alcohol which-must still have at least about 35 per cent of the then retically possible hydroxyl groups free and which must be water soluble to at least about one per cent by weight, and then to condensethis partial polyvinyl alcohol withthe aromatic aldehyde, but it .is equally possible to condense the polyvinyl alcohol with a mixture of aliphatic andaromatic aldehydes in finely dispersed state ina one-step procedure. The mixed. aliphatic-aromatic .acetal products are not necessarily better than those produced from aromatic aldehydes alone but the former may be less expensive owing to the fact that smaller proportions of-aromaticaldehyde are needed in the-production of the-mixed acetals.

It isbelieved evident from the above descrip,- tion that a wide selection of dyeing techniques can be used in the production of our pigments. It would be impossible within the scope of a patent specification to describeall of the diiferent procedures and dyes whichcan be used. But it is believed that we have described a sufiicient number of specific procedures to enable anyone skilled in the art todye our polyvinyl aromatic acetals satisfactorily with-any of the dyes falling within the scope of the following claims 'which possess the described common properties which seem to be essential for 'our purposes.

The pigments which are included in the present invention may be used for all purposes for which colored pigments are normally'used, such as the preparation of colored paints, artists colors, lacquers, varnishes, printing colors and coating compositions for the decoration of fabrics or paper, colored plastics and the like. In addition, these pigments can be used with or without the addition of other thermoplastic or thermosetting resins or resin forming compositions, fillers and plasticizers for the preparation of molded articles by the application of heat and pressure. The polyvinyl acetal pigments may-be mixed with known mineral or organic white or colored pigments; for instance, pale shadesmay be obtained from fully dyed polyvinyl pigments by admixture of a white mineralpigment, such as titanium dioxide. Pale shades may also be obtained directly by dyeing the polyvinyl'acetal with a (correspondingly) smaller amount of dyestufi; undyed polyvinyl acetal in finely dispersed form may be used as a white pigment. Mixed shades may be obtained by mixing a polyvinyl pigment with another polyvinyl pigment or with a pigment of a difierent type, or such mixed shades may be produced directly by dyeing-the finely dispersed polyvinyl acetal with two or nio're 'idyestufls wl'iichiiliavezamamnityi for-nit... :e'tl'ects may beobtaine byiincompletefimixing'iof a polyvinyl a'cetalipimentrwith anotherwpolymnyl acetal pigment and7orundyed. polyiiinylmacetal, followed 'by rm'ild-ingby heat and pressuren teapplioant's hereby disclaim i processes r whichtinvolve preparation oi the "finely-divided polyvinyl. aromatic *acetals, which areacoveredi by ttlheirrclirims, xi-ollowed by the-dyeing: xof these mammal. vat dyestuffs, as described and claimed 2N0.

' 215343086; and- 'followed by 'the dyeingslof 'these acetals with-a o dyes, as described andncclaimed in Ser. No. 50,252. Other modifioationswof i'lour invention. which fallwithin the scope of the followiiljgfclaimswilrbeimmediately evident to those. t

skilled inthisart.

What we claim is:

1. In the manufacture of finely-divided polyvinyl aromatic. acetals, the: process' which comprises, mixing under agitating conditions a. dilute; aqueous. polyvinyl alcohol. .solution, containing i dissolvedltherein from ralhnlithl. .to 20 per cent. of

a polyvinyl alcohol in which at least about 35 per cent of the theoretically possible hydroxyl groups are unsubstituted, with an aromatic aldehyde of the benzene and naphthalene series in the proportions of at least about 0.1 mole of aldehyde to 1 mole of polyvinyl alcohol, causing the aldehyde to condense with the polyvinyl alcohol in an aqueous reaction medium in which the acetal reaction product is so insoluble that it will precipitate as fast as it is formed, in the presence of an acetalizing catalyst and while the aldehyde is in a highly dispersed state, at temperatures above the freezing point of the solution but at least about 20 C. below the softening range of the resulting polyvinyl aromatic acetal, and recovering the finely divided solid polyvinyl aromatic acetal from the reaction mixture.

2. The process of claim 1 wherein the proportions of aromatic aldehyde and polyvinyl alcohol are controlled in the reaction medium so that at least about 20 per cent of the theoretically possible hydroxyl groups of the polyvinyl alcohol in the acetal formed in the process are left unsubstituted, whereby the polyvinyl aromatic acetals obtained are capable of being dyed.

3. The process of claim 1 wherein the molecu;

lar ratio of the aldehyde to the polyvinyl alcohol 5. The process of claim 1 wherein an emulsifying agent is present in the polyvinyl alcohol solution and wherein the aromatic aldehyde is emulsified in the solution as it is added thereto.

6. The process of claim 1 wherein the aromatic aldehyde is added to the polyvinyl alcohol solution in the form of an aqueous emulsion.

'7. The process of claim 1 wherein the aromatic aldehyde is a solid at the reaction temperatures and is emulsified by adding a solution thereof in a liquid aldehyde to the polyvinyl alcohol solution, thereby producing a mixed acetal.

8. The process of claim 1 wherein the polyvinyl alcohol is a partially hydrolyzed polyvinyl ester alcohol but contains no more than about 20 per cent of the original ester groups of the ester from which it was derived.

9. The process of claim 1 wherein the polyvinyl alcohol contains aliphatic acetal groups but not more than that corresponding to about 50 per 'thn thedndtioallyrethydmxyltnmups r :lyzed: pcl y-yinylk :esten containing. nonmore than .aboutidiperscentiof itheroniginallvestemgmupsz 11. In the amanutacture :oii'polyvinyharomatic acetals capable of being dyed to produce organic pigmentathe process which comprises mixing a dilute. aqueous: polyvinyl alcohol solution, containingufrom about. 1. .to v per. cent by. weight of a polyvinylalcohol inwhichatleast about per cent of the theoretically possible hydroxyl groups-are unsubstituted, withian aromatic aldehyde 'of the. benzene and naphthalene series in molecular proportions within the range-of from product atfleastj about? 20' per cent. .of the. theogret'ically possible hydroxyl groups ofithe polyvinyl alcohol'jresidueare leftifree,,,caus'ing .tlie aldehyde to condense with the polyvinyljalcoholfin .anaquecos reaction medium in which the acetal" reaction product is so insoluble that it will precipitate as fast as it is formed, in the presence of an acetalizing catalyst while in a highly dispersed state while agitating and maintaining the temperature of the reaction mixture within the range of from about 1 to 80 0., thereby producing a. finely-divided solid polyvinyl aromatic: acetal.

12. The process of claim 11 wherein the polyvinyl alcohol contains no more than about 20 per cent of aliphatic ester groups and no more than about per cent of aliphatic acetal groups, expressed in terms of the theoretically possible hydroxyl groups in the polyvinyl alcohol.

13. As a new product, a polyvinyl aromatic acetal capable of being dyed with organic dyestuffs containing at least one substituent group selected from the class consisting of amino groups, phenolic hydroxyl groups and. enolic hydroxyl groups, which acetal contains aromatic acetal groups and free hydroxyl groups and which may contain low-molecular aliphatic ester groups r and aliphatic acetal groups falling within the ranges indicated in the following table and as expressed in terms of the theoretically possibly hydroxyl groups of the polyvinyl residue in said acetal:

Ester Aromatic Alinlmflr- Total Free Groups Acetal Acetal Acetal Hydroxyl Percent Percent Percent Percent Percent Up to 5 30-70 0 30-70 05-25 20 20-60 0 20-60 -20 Up to .5 20-70 50-5 -25 70-20 20 15-60 30-5 60-20 60-20 said polyvinyl aromatic acetal having an average particle size within the range of from about 0.5 to 5 microns with substantially no particles over 20 microns, having softening points within the range of from about to 0., being insoluble in water, ether, petroleum fractions, and aromatic hydrocarbons but freely soluble in benzyl alcohol, tetrahydrofurfuryl alcohol, dioxane, m-cresol, aniline, m-toluidine, p-xylidine and cyclohexylamine, their solubility in organic solvents increasing with increase in acetal group content, having a high affinity for organic dyestuffs of the type stated and capable of being molded under the action of heat and pressure.

14. A dyed polyvinyl aromatic acetal suitable for use as a pigment or molding powder. which 1 acetal contains aromatic acetal groups and free molecular aliphatic ester groups and aliphatic acetal groups falling within the ranges indicated in the following table and as expressed in terms of the theoretically possible hydroxyl groups of the polyvinyl residue in said acetal:

Ester Aromatic Aliphatic Total Free By- Groups Acetal Aeetal Acetal droxyl Percent Percent Percent Percent Percent Up to 5 30-70 30-70 65-25 20 20-60 0 20-60 00-20 Up to -70 -5 -25 70-20 20 15-60 30-5 60-20 60-20 said acetal having an average particle size within the range of from about 0.5 to 5 microns with substantially none over 20 microns, having softening points within the range of from about to 0., being insoluble in water, ether, petroleum fractions and aromatic hydrocarbons but 24 freely soluble in benzyl alcohol, tetrahydrofurfuryl alcohol, dioxane, m-cresol, aniline, m-toluidine, p-xylidine and cyclohexylamine, being readily moldable under the action of heat and pressure and dyed with an organic dye, with the exception of vat dyestuffs and azo dyes, having at least one substituent group in the molecule selected from the class consisting of amino groups, phenolic hydroxyl groups and enolic hydroxyl groups and having a solubility in water ranging from about 0.01 to 1.5 per cent by weight, the color being exceptionally bright and substantially fast to light.

LOUIS AMEDEE LANTZ.

ARTHUR SCHOFIELD.

References Cited in the file of this patent UNITED STATES-PATENTS Number Name Date 2,269,216 McNally Jan. 6, 1942 2,534,136 Lantz et a1. Dec. 12, 1950 

1. IN THE MANUFACTURE OF FINELY-DIVIDED POLYVINYL AROMATIC ACETALS, THE PROCESS WHICH COMPRISES MIXING UNDER AGITATING CONDITIONS A DILUTE AQUEOUS POLYVINYL ALCOHOL SOLUTION, CONTAINING DISSOLVED THEREIN FROM ABOUT 1 TO 20 PER CENT OF A POLYVINYL ALCOHOL IN WHICH AT LEAST ABOUT 35 PER CENT OF THE THEORETICALLY POSSIBLE HYDROXYL GROUPS ARE UNSUBSTITUTED, WITH AN AROMATIC ALDEHYDE OF THE BENZENE AND NAPHTHALENE SERIES IN THE PROPORTIONS OF AT LEAST ABOUT 0.1 MOLE OF ALDEHYDE TO 1 MOLE OF POLYVINYL ALCOHOL, CAUSING THE ALDEHYDE TO CONDENSE WITH THE POLYVINYL ALCOHOL IN AN AQUEOUS REACTION MEDIUM IN WHICH THE ACETAL REACTION PRODUCT IS SO INSOLUBLE THAT IT WILL PRECIPITATE AS FAST AS IT IS FORMED, IN THE PRESENCE OF AN ACETALIZING CATALYST AND WHILE THE ALDEHYDE IS IN A HIGHLY DISPERSED STATE, AT TEMPERATURES ABOVE THE FREEZING POINT OF THE SOLUTION BUT AT LEAST ABOUT 20* C. BELOW THE SOFTENING RANGE OF THE RESULTING POLYVINYL AROMATIC ACETAL, AND RECOVERING THE FINELY DIVIDED SOLID POLYVINYL AROMATIC ACETAL FROM THE REACTION MIXTURE. 